Abstract:

The present invention relates to random form of nanoscale silicate plates
produced by a process using an exfoliating agent. The exfoliating agent
used in the present invention has the formula:
##STR00001## where n=1 to 5wherein n=1 to 5 and R is a
polyoxypropylene group, poly(oxyethylene/oxypropylene) group, or
polyoxyethylene group. In this invention, layered silicate clays are
exfoliated into random silicate plates by acidifying AMO with inorganic
acid, adding the acidified AMO to layered silicate clay with agitation,
and adding sodium hydroxide or chloride of alkali metal or alkaline-earth
metal, in ethanol, water and a hydrophobic organic solvent to the
intermediate product and repeating phase separation procedures to isolate
random silicate plates from water phase.

Claims:

1. A random form of nanosilicate plates produced by a process comprising
the steps of:(a) preparing amine-terminating Mannich oligomers (AMO) from
polyoxyalkylene diamine, p-cresol and formaldehyde to obtain a polymeric
exfoliating agent having a general formula: ##STR00011## where n=1 to
5wherein n is from 1 to 5; R represents an organic group selected from
the group consisting of polyoxypropylene groups,
poly(oxyethylene/oxypropylene) groups, and polyoxyethylene groups;
wherein said formaldehyde is added at an appropriate addition rate by
which the exothermic temperature is kept below 120.degree. C.;(b) adding
inorganic acid to said AMO to form an acidified AMO;(c) mixing said
acidified AMO with a swelled inorganic layered silicate clay so as to
exfoliate said silicate clay directly through cationic exchange to form
an exfoliated silicate clay;(d) mixing an aqueous solution containing a
hydroxide or a chloride of alkali metal or alkaline-earth metal, ethanol,
water and an organic solvent with said exfoliated silicate clay obtained
in step (c) to form a mixture; and(e) keeping the mixture obtained in
step (d) static to form an upper organic phase and a lower water phase
containing nanosilicate plates.

2. The random form of nanosilicate plates as claimed in claim 1, wherein
said polyoxyalkylene diamine used in said step (a) has molecular weight
ranging from 400 to 4,000 g/mol.

3. The random form of nanosilicate plates as claimed in claim 1, wherein
said polyoxyalkylene diamine used in said step (a) has molecular weight
ranging from 1,000 to 2,000 g/mol.

4. The random form of nanosilicate plates as claimed in claim 1, wherein
said polyoxyalkylene diamine used in said step (a) is selected from the
group consisting of polyoxypropylene diamine, polyoxyethylene diamine,
polyoxybutylene diamine and poly(oxyethylene-oxypropylene) diamine.

5. The random form of nanosilicate plates as claimed in claim 1, wherein
said polyoxyalkylene diamine used in said step (a) is polyoxypropylene
diamine.

6. The random form of nanosilicate plates as claimed in claim 1, wherein
said polyoxyalkylene diamine, p-cresol and formaldehyde in said step (a)
are added at a molar ratio (n+1):n:2n, wherein n is 1 to 5.

7. The random form of nanosilicate plates as claimed in claim 1, wherein
said formaldehyde used in said step (a) is added at a reaction
temperature in the range of 25.degree. C. to 120.degree. C.

8. The random form of nanosilicate plates as claimed in claim 1, wherein
25.about.100 wt % of said exfoliating agent obtained in said step (a) has
molecular weight ranging from 9,000 to 20,000.

9. The random form of nanosilicate plates as claimed in claim 1, wherein
said exfoliating agent and said inorganic acid are mixed in an equivalent
ratio 2:1 in said step (b).

10. The random form of nanosilicate plates as claimed in claim 1, wherein
said inorganic acid used in said step (b) is selected from the group
consisting of hydrochloric acid, sulfuric acid, phosphoric acid and
nitric acid.

11. The random form of nanosilicate plates as claimed in claim 1, wherein
the molar ratio of amino groups in said exfoliating agent to cationic
exchange capacity of said silicate clay ranges from 3:1 to 1:1 in said
step (c).

12. The random form of nanosilicate plates as claimed in claim 1, wherein
said silicate clay used in said step (c) is selected from the group
consisting of montmorillonite, kaolin, mica and talc.

13. The random form of nanosilicate plates as claimed in claim 1, wherein
said silicate clay used in said step (c) has a cationic exchange capacity
ranging from 50 meq/100 g to 200 meq/100 g.

14. The random form of nanosilicate plates as claimed in claim 1, wherein
said hydroxide or chloride of alkali metal or alkaline-earth metal used
in said step (d) is sodium hydroxide.

15. The random form of nanosilicate plates as claimed in claim 1, wherein
said hydroxide or chloride of alkali metal or alkaline-earth metal is
added at the same equivalence in said step (d).

16. The random form of nanosilicate plates as claimed in claim 1, wherein
said organic solvent used in said step (d) is selected from the group
consisting of ether, ketone, ester, nitrile, saturated hydrocarbon,
chlorinated hydrocarbon, saturated hydrocarbon and aromatic hydrocarbon.

18. The random form of nanosilicate plates as claimed in claim 1, wherein
said hydroxide or chloride of alkali metal or alkaline-earth metal is
added at 1 to 5 equivalences in step (d).

19. The random form of nanosilicate plates as claimed in claim 1, wherein
said organic phase formed in said step (e) comprises said exfoliating
agent suitable for recycling.

20. The random form of nanosilicate plates as claimed in claim 1, wherein
solid content in the water phase formed in said step (e) is from 0.1 to
90 weight percent.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is a divisional application of prior U.S.
application Ser. No. 11/164,165, filed Nov. 13, 2005, which is now
pending and is a divisional application of prior U.S. application Ser.
No. 10/685,213, filed Oct. 14, 2003, which has issued as U.S. Pat. No.
7,125,916 on Oct. 24, 2006.

[0005]Currently, inorganic/organic polymer composite materials in a
nanometer scale regime (approximately 1˜100 nanometer scale) are
one of the most important materials, and thus have been widely
investigated and developed. Such nanocomposite materials have two
different phases including inorganic and organic components, wherein at
least one phase is dispersed under a nanoscale regime in a homogeneous
manner. Accordingly, the compatibility in the nanoscale mixing between
two distinct phases, for example, inorganic clay and organic polymer, is
the essential factor for the nanocomposite's physical and mechanical
performance. In general, the clay/polymer hybrid materials can be
classified into two categories of composites, the intercalated and the
exfoliated, on the basis of the clay dispersion in polymer matrix. In an
intercalated structure, the silicate plates still maintain their layered
structure but with the addition of organic intercalants anchored in the
gallery. In the exfoliated form, each individual silicate plate is
randomly dispersed in the polymer matrix. Dramatically improved physical
properties are often obtained for the exfoliated structure, as
demonstrated by the first commercialized Nylon6/montmorillonite
nanocomposites. In such a system, the silicate plates (about
100×100×1 nm in dimension) are well-entangled with polymer
strands through van der Waals forces and evenly distributed in the
polymer matrix. Only a low percentage of exfoliated silicate plates is
required to enormously improve the mechanical and physical properties of
the blended material.

[0006]Since the naturally occurring layered silicate clays are
hydrophilic, the dispersion of clay in polymer matrix on a nanometer
scale is a general problem. The process requires an enlargement of the
clay interlayer distances by means of organic quaternary ammonium
incorporation, and thus monomers can enter into the clay interface
through ionic exchange reactions. The monomers can then be polymerized
within the interlayer space to obtain an exfoliated inorganic/organic
polymer nanocomposite material. In principle, the enlarged distance is
preferred to be wide enough for monomer or polymer molecules to enter.
After exfoliation, the layered structure is randomized into irregular
shapes and the silicate plates have different directions without any
crystalline form. The random silicate plates are therefore dispersed in
organic polymers as nanocomposites.

[0007]Conventional intercalating agents such as 12-aminol auric acid,
hexadecylamine, fatty amine, bis(2-hydroxyethyl)methyl tallow alkyl amine
and stearylamine, usually have low molecular weights and can be converted
into the corresponding ammonium salts such as quaternary ammonium
chloride salt. Through ionic exchange reactions, the counter ions in
interlayer spaces of the clay can be ionically exchanged and hence the
interlayer distance expanded to a certain degree.

[0008]Referring to the research of T. J. Pinnavaia (Michigan State
University), intercalating agent CH3(CH2)n--NH3+
is provided to exchange with metal ion salts within the layer-structured
montmorillonite clay (MMT) in preparing intercalated and organic modified
MMT, which is then dispersed in diglycidyl ether of bisphenol-A (such as
epoxy resin Shell Epon 828) to form a epoxy polymer-clay composite
material in a nanoscale dispersion. By using such intercalating agents,
the interlayer distances of MMT can be enlarged to 18.0 Å. The epoxy
resin can then enter into the interlayer and form an epoxy/clay material
through curing polymerization at 75° C. This reference also
indicates an improvement in heat distortion temperature. The
intercalating agent performs a role of monolayer to bilayer, and even to
pseudo-trilayer. The interlayer distance ranges between 13.8-18.0 Å,
which allow the epoxy resin to polymerize therein, and further to
exfoliate the layered inorganic matter so that performance advantages are
achieved.

[0009]Japanese Patent No. 8-22946 (Toyota Company) discloses the first
commercial inorganic/organic polymer composite material under a nanoscale
regime. This composite material is produced by dispersing
[H3N+(CH2)11COO.sup.-]-montmorillonite in Nylon 6,
wherein the aminocarboxylic acid is provided as an intercalating agent
and the polymers are formed between layers of the aminoacid intercalated
clay through condensation of caprolactam monomers to Nylon 6 polymer. In
this invention, since the aminocarboxylic acid intercalating agent is
hydrophilic, the modified clay is suitable for Nylon 6 compatibility but
can not easily mix with nonpolar polymers such as polyethylene and
polypropylene in an uniform manner. Accordingly, Japanese Patent
Publication No. 8-53572 provides other organic onium ions as an
intercalating agent to mix with layered silicate, which can be uniformly
dispersed in molten polyolefin resin. Unfortunately, the organic onium
ions can only enlarge the interlayer distances to a certain degree and
the affinity between the intercalating agent and the polyolefin resin is
too weak to exfoliate the layered silicates.

[0010]In general, the difficulty for the exfoliation by using conventional
quaternary ammonium salt is caused by the inherent chemical structure of
the clay. The chemical structure of the common smectite clays such as
montmorillonite consists of ionic pairs of ≡Si--O.sup.- anions on
the surface and counter metal cations. The surface ionic charge
interaction tightly binds the neighboring silicate plates together and
maintains the primary stacking structure. The exfoliation of the layered
silicate plates hence requires a tremendous force to overcome the
inherent ionic bridges. Moreover, the conventional process requires two
separate steps. The layered silicates are first ionically exchanged with
an intercalating agent such as amino acid, or alkyl ammonium quaternary
salt. The intercalated silicates at this stage are embedded with organic
salts and the gallery distance is widened to a commonly 18-40 Å. In
the presence of organic intercalants, the modified clays become
organophilic and are possibly exfoliated. Accordingly, there is a need to
ameliorate the process by means of providing appropriate intercalating
agents and operation conditions which may exfoliate the silicate clay
directly for better compatibility with other polymer materials. In
addition, it is even more desired to prepare the exfoliated form of
silicate plates which are free of organic polymers, so that the random
silicate plates in pure form and free of organic contaminations can be
mixed with different target polymers to produce improved properties
without encountering the dispersion problem in the process.

BRIEF SUMMARY OF THE INVENTION

[0011]The main object of the present invention is to provide a method for
producing random nanoscale silicate plates, in which the layered clay
structure may be exfoliated directly by an exfoliating agent to produce
random nanosilicate plates.

[0012]Another object of the present invention is to provide a method for
producing random nanosilicate plates, whereby the organic exfoliating
agent can be recycled through sodium ion exchange and the random silicate
plates may be isolated in water suspension without organic contamination.

[0013]The present invention involves a multiple-step process: (a)
acidifying the exfoliating agent with an inorganic acid to form a
quaternary ammonium salt; (b) mixing the acidified exfoliating agent with
a swelled inorganic silicate clay so as to exfoliate the clay directly
through cationic exchange reaction; (c) adding an aqueous solution
containing a hydroxide or a chloride of alkali metal or alkaline-earth
metal, ethanol, water and an organic solvent, and then keeping the
mixture static to form an upper organic phase and a lower water phase
containing the nanosilicate plates, and isolating the lower water phase.
The random nanosilicate plates, dispersed in the water phase, contain no
impurity and therefore are suitable for further application in modifying
polymers.

[0014]In order to achieve the above objects, the process of the present
invention requires the preparation of the novel exfoliating agents
optionally from one of the following synthesis methods:

[0015](1) preparing amine-terminated Mannich oligomers (AMO) from
polyoxyalkylene diamine, p-cresol and formaldehyde at a molar ratio of
(n+1):n:2n, where n=1 to 5, the AMO having a general formula:

##STR00002##

[0016]where n=1 to 5

[0017](2) preparing amine-terminated epoxy oligomers (AEO) from the epoxy
opening reaction of polyoxyalkylene diamine and diglycidyl ether of
bisphenol-A at a molar ratio of (m+1):m, where m=1 to 5, the AEO having
the formula:

##STR00003##

[0018]where m=1 to 5wherein the polyoxyalkylene diamine has the formula:

##STR00004##

[0018]where x=2 to 120 or the molecular weight is in the range of 200 to
8,000.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic diagram illustrating the steps of the method
producing nanosilicate plates in this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020]The method for producing random nanoscale silicate plates of the
present invention can be exemplified by the following process block
scheme, illustrating a general process starting with AMO or AEO. The
overall process comprises (1) acidifying the exfoliating agent with an
inorganic acid to form quaternary ammonium salt; (2) mixing the acidified
exfoliating agent with a swelled inorganic silicate clay so as to
exfoliate the clay directly through cationic exchange reaction; (3)
adding an aqueous solution containing a hydroxide or a chloride of alkali
metal or alkaline-earth metal, ethanol, water and an organic solvent, and
then keeping the mixture static to form an upper organic phase and a
lower water phase containing the nanosilicate plates, and isolating the
lower water phase.

[0021]The following steps are illustrated in FIG. 1. In step 1, the
polyamine exfoliating agent is pretreated with a controlled amount of
inorganic acid to produce quaternary ammonium salts in water emulsion.
The equivalent ratio of the exfoliating agent to the inorganic acid is
preferably 2:1 with respect to amine equivalent to acid, wherein the
inorganic acid can be hydrochloric acid, sulfuric acid, phosphoric acid,
nitric acid, etc.

[0022]In step 2, the acidified polyamine exfoliating agent, in the form of
quaternary ammonium salt with multiple cation reactive sites, is added to
layered silicate clay, which is pretreated with water for swelling. In
the following step, the inorganic clay is added with vigorous agitation
to facilitate the ionic exchange reaction between the quaternary salts
and the sodium ions of the clay. The molar ratio of amino groups in the
exfoliating agent to cationic exchange capacity of the silicate clay is
preferably between 1:1 and 3:1.

[0023]The clay is selected from one of the following naturally occurring
smectite clays, including montmorillonite, kaolin, mica, layered double
hydroxide, (J. H. Choy, S. Y. Kwak, Y. J. Jeong, J. S. Park, Angew. Chem.
Int. Ed. 39, 4041(2000), M. Templin, A. Franck, A. D. Chesne, H. Leist,
Y. Zhang, R. Ulrich, V. Schadler, U. Wiesner, Science 278, 1795 (1997),
M. B. Armand, in Polymer electrolyte reviews-1 (eds J. R. Maccallum, C.
A. Vincent,) (Elsevier applied science, New York and London, 1987), etc.,
and preferably has a cationic exchange capacity ranging from 50 meq/100 g
to 200 meq/100 g. Among the inorganic layered silicate clay, sodium
montmorillonite (Na+-MMT) is used in the preferred embodiment. The
clay may be commercially purchased from Nanocor, Southern Clay, Kunimine
Industries Co. The structure is composed of primary structure containing
8-10 layers of lamellae silicate as the fundamental unit and secondary
structure containing the aggregates of primary units. In the primary
units, each layer of the lamellae is about 9.6-10 Å thick and the
interlayer distance is about 12 Å. The size of the silicate
aggregates usually ranges form 0.1μ to 10μ, which is required to be
swelled with water to form a slurry beforehand.

[0024]In step 3, the hydroxide or chloride of alkali metal or
alkaline-earth metal is preferably sodium hydroxide, and added at the
same equivalence. More preferred alkali salts are sodium hydroxide,
potassium hydroxide, lithium hydroxide, cesium hydroxide, calcium
hydroxide, magnesium hydroxide, aluminum hydroxide and their mixtures or
derivatives. The alkali compound provides alkalinity to neutralize or
convert the quaternary ammonium salt to amine. Consequently, the emulsion
is broken and a two-phase solution is formed. The alkaline salt is
preferably added in excess amount, for example, at double or triple
equivalence to the original clay CEC value. The organic phase formed in
step 3 contains the AMO or AEO exfoliating agents which can be easily
phase separated from the water phase and then recycled.

[0026]The random nanosilicate plates existing in the water phase as
obtained in step 3 usually contain no impurity and therefore are suitable
for further application in modifying polymers.

[0027]It has been discovered that the process for direct exfoliation in
accordance with the present invention requires the synthesis of novel
exfoliating agents which may be prepared by using the following raw
materials and chemicals used in experimental examples cited.

[0028]The polyoxyalkylene diamines to be used as starting materials in
accordance with the present invention are poly(propylene glycol)
bis(2-aminopropyl ether)s having the formula:

##STR00006##

wherein x is a positive number having a value from 2 to 70.

[0029]Representative amines have an average molecular weight of about 230
wherein the value of x is between 2 and 3 (Jeffamine® D-230), an
average molecular weight of about 400 wherein the value of x is between 5
to 6 (Jeffamine® D-400), an average molecular weight of about 2000
wherein the value of x is about 33 (Jeffamine® D-2000) and an average
molecular weight of about 4000 wherein the value of x is about 68
(Jeffamine® D-4000). All of these polyoxyalkylene diamines are
commercial products and can be purchased from: Huntsman Chemical Co. USA,
or from Aldrich Chemical Co. These starting materials are
polyoxypropylene-backboned and primary amine terminated diamines.

[0030]In accordance with the present invention, the required exfoliation
agents are prepared by the following sequence:

[0031]A polyoxypropylene diamine having the composition as described in
the above formula is dissolved in toluene and added with p-cresol at a
specified equivalent ratio. The reaction mixture thus formed is heated to
30-60° C. and added with formaldehyde at the preferred molar ratio
of polyoxyalkylene diamine, p-cresol and formaldehyde at (n+1):n:2n,
where n=1 to 5, to obtain a polymeric exfoliating agent, amine
terminating Mannich oligomer (AMO). The polyoxypropylene diamine is
preferred to have a molecular weight ranging from 200 to 8,000 g/mol, and
the formaldehyde is added at a slow rate to avoid the exothermic
temperature over 120° C.,

##STR00008##

[0032]where n=1 to 5

[0033]In the present invention, the polyoxyalkylene diamine preferably has
molecular weight ranging from 200 to 8,000; and more preferably from 400
to 2,000 and even more preferably from 1,000 to 2,000. Polyoxyalkylene
diamine can be, for example, polyoxypropylene diamine, polyoxyethylene
diamine, poly(oxyethylene-oxypropylene)diamine, polyoxybutylene diamine,
etc., wherein polyoxypropylene diamine is preferred. A generic chemical
structure is depicted below, where x=2 to 120 or the molecular weight is
in the range of 200 to 8,000.

##STR00009##

[0034]In the above steps, formaldehyde is preferably added at an
equivalent ratio ranging from 0.5 to 2.0 molar ratio to amine, whereby
more than 25 wt % of the total AMO copolymers have molecular weight more
than 5,000 and less than 10,000 g/mol.

[0035]Optionally, the polymeric polyamine exfoliating agent may be of
another class of compound, namely the amine terminated epoxy oligomers
(AEO), which may be prepared from the epoxy opening reaction of
polyoxyalkylene diamine and diglycidyl ether of bisphenol-A at a molar
ratio of (m+1):m, where m=1 to 5, wherein the polyoxyalkylene diamine has
a molecular weight ranging from 200 to 8,000 g/mol and preferably 400 to
2,000 g/mol.

##STR00010##

[0036]where m=1 to 5

[0037]In this invention, by means of cationic exchange reaction between
AMO or AEO and sodium montmorillonite, interlayer distances of the clay
are enlarged through intercalation and eventually exfoliation to silicate
plates in a random manner. However, the ionic bridges between AMO or AEO
and individual silicate plates still exist in a form of the quaternary
ammonium salt/clay complex. In order to separate the exfoliated silicate
plates from the organic exfoliating agents, an aqueous solution of
alkaline metal hydroxide such as sodium hydroxide is added into the
hybrids to exchange the organic quaternary ammonium cations with sodium
ions. The random nanosilicate plates can then be isolated in water
suspension. The process requires repetitive displacement reactions for
several times by adding solvent mixtures of ethanol/water/toluene. The
extraction step requires an appropriate solvent composition which causes
the two-phase separation, with the AMO or AEO amines in the upper toluene
phase and the nanosilicate plates suspension in the lower water phase.
For the overall process, the purified nanosilicate plate suspension in
water can be obtained and the AMO or AEO exfoliating agent is recycled.

[0038]More detailed procedures of the present invention are described in
the preferred Examples and the Comparative Examples.

Example 1

Exfoliation of Na+-MMT by Using AMO Agent

[0039]Sodium montmorillonite (Na+-MMT) (10 g, 11.5 meq) is
preliminarily dispersed in water (1 L, 80° C.) in a beaker and
swelled by vigorously stirring for 4 hours to form an earth-colored
uniform dispersion before the ionic exchange reaction. The following
illustrates the experimental procedures which are performed in a glass
reactor equipped with a mechanical stirrer, a thermometer, a condenser, a
heating mantle and temperature controller.

[0040]To Prepare the amine-terminating Mannich oligomer (AMO) as the
exfoliating agent, to a reactor, p-cresol (13.6 g, 126 mmoles) and
poly(propylene glycol)diamine (Jeffamine D-2000, 378 g, 189 mmole) were
dissolved in toluene (200 ml) and the mixture was heated to 90° C.
for 3 hours. Formaldehyde (37 w % in water, 30 g, 278 mmole) is then
gradually added in a duration of 4.5 hours, at a rate of about 6-7.5
ml/hour. During the process, the solution temperature was exothermic up
to 90° C.-130° C. Stirring continuously for 5 hours, a very
viscous product was obtained. According to the gel permeation
chromatography (GPC) analysis, three major peaks at Mw 3,100, Mw 6,200
and Mw 9,200 were observed, on the basis of polystyrene as the GPC
standard. Amine titration values of the AMO product are 0.4 meq/g for
primary amine and 0.56 meq/g for secondary amine, and none for tertiary
amine, indicating the formation of Mannich secondary amine and the
conversion of primary amine into the desired products.

Step (1): Acidification of the AMO Exfoliating Agent

[0041]The AMO product (57.5 g; 23 meq) was not completely soluble in
water. With the addition of concentrated hydrochloric acid (35 w % in
water, 1.2 g; 11.5 meq), the product became soluble or formed an emulsion
solution at 80° C. after being stirred for 30 minutes. The AMO
quaternary salt was hence prepared for the MMT exfoliation.

Step (2): Exfoliation of Sodium Montmorillonite Clay

[0042]The acidified AMO emulsion (from Step 1) was poured into the
pre-prepared dispersion of Na+-MMT in water at 80° C. while a
vigorous agitation was continued for over 5-hour period. After standing
at room temperature, the AMO/MMT hybrid was isolated by separating the
floating solid material from the water phase. A sample of the isolated
hybrid was analyzed by X-ray diffraction and shown to have none of
crystalline phase (exfoliation).

[0043]To the AMO/MMT hybrid (from Step 2), which was dispersible in
toluene and ethanol but not in water, was directly added an aliquot of
aqueous NaOH (4.6 g in water). With agitation, the mixture became a
cream-colored thick suspension. The solid suspension was filtrated and
washed by mixing with ethanol (750 ml). A second washing procedure was
performed by adding and stirring with another portion of ethanol (1 L)
and filtrated again to obtain a cream-colored translucent AMO/NSP
(nanosilicate plate) hybrids. The hybrid was analyzed by thermal
gravimetric analysis, the result of which indicated an organic (AMO)
composition of 40 weight %.

[0044]A second displacement reaction was carried out to remove organic AMO
exfoliating agent completely. In this step, the procedure was repeated by
mixing the above AMO/NSP hybrid product with another portion of NaOH (9.2
g) in ethanol (1 L), water (1 L), and toluene (1 L). After vigorously
stirring and standing for overnight, the mixtures were phase separated
into an upper toluene phase containing the AMO exfoliating agent, a
middle phase of clear ethanol, and a lower water phase containing
nanosilicate plates (NSP). The AMO copolymers in toluene phase can be
easily isolated by solvent evaporation and recycled.

Comparative Example 1

[0045]The above experimental procedures were repeated but using only a
half amount of AMO exfoliating agent prepared from the Mannich reaction
of p-cresol, poly(propylene glycol)diamine and formaldehyde. The
resultant AMO/MMT from the Step (3) was analyzed by X-ray diffraction
(XRD) which indicated that the basal spacing was 50 Å, indicative of
the MMT in an AMO intercalating mode rather than exfoliation. The result
demonstrates the importance of AMO copolymer amount used for the
exfoliation and the preparation of nanosilicate plates.

[0047]The experimental procedures of Example 1, Steps 1-3, were repeated
but using a different synthesis of exfoliating agent (abbreviated AMO-1),
and repeating the synthesis for the amine-terminating Mannich oligomers
(AMO). The Mannich reaction was repeated with the same equivalent ratio
of starting materials and reaction temperature, but the formaldehyde was
added to the p-cresol, poly(propylene glycol)diamine (Jeffamine D-2000)
in one-portion rather than dropwise. The resultant AMO-1 was analyzed and
the result exhibited a lower molecular weight distribution than that of
AMO in Example 1. The GPC analysis indicated also three peaks at Mw 670,
Mw 3,000 and Mw 6,000, on the basis of polystyrene standard.

[0048]By following the procedures in Step (2), the resultant AMO-1/MMT
exhibited a XRD basal spacing (56 Å) rather than an exfoliating
non-crystalline pattern. By continuing the Step (3), the solid became a
cream-colored suspension and the AMO-1 polyamine cannot be separated from
MMT, since both organics and inorganics were present in the toluene
phase. The results indicated that the low molecular weight of AMO-1
rendered an intercalated MMT complex rather than an exfoliated MMT. As a
consequence, the inorganic MMT and organic AMO-1 cannot be separated.
Hence it is important for AMO to have a suitable molecular weight for
exfoliating layered silicate into random silicate plates.

Comparative Examples 3-5

[0049]The experimental procedures of Example 1 were repeated from Step (1)
to Step (3). In the step (3), the two phase solvent was toluene/water
without the addition of ethanol. It is found the hybrid product can not
be filter due to the high viscous and sticky nature of the product. It is
realized that the proper mixture of solvent including ethanol is required
to isolate the random silicate plates in the process.

Example 2

A Larger Scale Experiment

[0050]Sodium montmorillonite (Na+-MMT 100 g, cationic exchange
capacity 115 mequiv/100 g) was dispersed into 10 L of hot water (about
80° C.) by using a homogenizer. Amine terminating-Mannich Oligomer
(AMO) was dissolved in water (575 g) and concentrated hydrochloric acid
(35 wt % in water 12 g) were mixed at 80° C. for 30 minutes. The
GPC analysis of high Mw AMO used in Example 2 shows three peaks at 4,000,
8,100 and 12,600. The solution was poured into the hot aqueous dispersion
of Na+-MMT/Water with a vigorous agitation for 5 hours at 80°
C. to complete the intercalation. The solution becomes phase separated.
Repeat procedures of Example 1, but all the materials are added in
quantities ten time as much. The same nanosilicate plates as Example 1
can be eventually obtained.

[0051]In the Comparative Examples 1, 3, 4 and 5 using the molar ratio of
AMO exfoliating agent at one or less than one equivalent to clay CEC, the
results showed the intercalating clay. Only at 2:1 excess amount of the
same AMO, the clay may be exfoliated.

[0052]As indicated in the above Examples 1 and 2, the preparation of
random silicate plates can be performed by using an AMO quaternary
ammonium salt as the exfoliating agent. The process required several
steps including exfoliation, sodium hydroxide exchange and phase
toluene/ethanol/water extraction. The controlled experiments demonstrated
that the AMO molecular weight, molecular structure, phase extraction
solvent and sodium hydroxide equivalent are crucial parameters for
effectively producing random silicate plates. The nanosilicate plates
produced in the present invention are primary structure and exhibit ionic
character and high-aspect ratio (surface versus thickness) properties,
which are suitable for improving physical/mechanical properties of
polymers, for example, resistance to solvent, resistance to heat
distortion, gas barrier properties, rigidity, etc.

Example 3

Exfoliation of Na+-MMT by Using AEO Agent

[0053]The following experimental procedures are a typical example for the
preparation of AEO exfoliating agent and its uses for ionic exchanging
with Na+-MMT clay.

[0054]To a glass reactor was added poly(propylene glycol)diamine
(Jeffamine D-2000, 320 g, 160 mmoles) and diglycidyl ether of bisphenol-A
(38 g, 100 mmoles) dissolved in toluene (500 ml) and the mixture was
heated to 90° C. for 3 hours. The temperature was slowly increased
until all solvent was removed from a trap condenser. The resulting
product was a viscous and yellowish liquid. The polymeric amines were
further analyzed by amine titration and GPC (three peaks at 660, 1,900,
and 6,000) to confirm the oligomeric structure. The conversion of primary
amines into secondary amines through the reaction with DGEBA was
evidenced by amine titration, showing 0.36 meq/g for primary amine
(theoretical 0.33 meq/g) and 0.67 meq/g for secondary amine (theoretical
0.66 meq/g). The polymeric amine was used for the following exfoliation
process.

Step (1): Acidification of the AEO Exfoliating Agent

[0055]The AEO product prepared in the above synthesis (64 g) was not
completely soluble in water. With the addition of concentrated
hydrochloric acid (35 w % in water, 2.5 g), the product became soluble or
formed an emulsion solution at 80° C. after being stirred for 30
minutes. The AEO quaternary salt was hence prepared for the MMT
exfoliation.

Step (2): Exfoliation of Sodium Montmorillonite Clay

[0056]The acidified AEO emulsion obtained from Step (1) was poured into a
suspension of Na+-MMT (20 g, CEC=120 meq/100 g) in water at
80° C. while a vigorous agitation was continued for over 5 hour
period. After adding ethanol (100 ml) and standing at room temperature,
the AEO/MMT hybrid was isolated by separating the floating solid material
from the water/ethanol phase. A sample of the isolated hybrid was
analyzed by X-ray diffraction and shown to have none of crystalline phase
(exfoliation).

[0057]To the AEO/MMT hybrid obtained in Step (2), which was dispersible in
toluene and ethanol but not in water, was directly added an aliquot of
aqueous NaOH (2.4 g in water). With agitation, the mixture became a
cream-colored thick suspension, to which ethanol (500 ml) was added. A
second washing procedure was performed by adding and stirring with
another portion of ethanol (500 ml) and filtrated again to obtain a
cream-colored translucent AEO/NSP (nanosilicate plate) hybrids. The
second washing procedure was repeated by adding another portion of NaOH
(2.4 g in 25 ml water), ethanol (300 ml) and toluene (150 ml). The
mixture was agitated and stood for phase separation. A three-layer
suspension was obtained and the bottom water layer contained nanosilicate
plates.